In motion pictures, lighting may be used not only to help actors and sets look their best, but as an integral part of storytelling to set mood, direct attention, and underscore performance. The importance of lighting may be reflected in the high proportion of time and expense spent on lighting: by some estimates, one half or more of the valuable time spent on a set may be involved in setting up the lighting.
Several aspects of film production may be performed after principal photography, such as editing, sound effects, scoring, color correction, and visual effects. In each case, the fact that the process can be performed as part of postproduction may allow results to be progressively improved and revised by the filmmakers after principal photography. Lighting, in contrast, may in large part have to be finalized at the time each scene is filmed. This requirement may add complication and cost to principal photography, and may provide limited options for modification and improvement during postproduction. A situation where this is a particularly difficult constraint may occur when shooting actors in front of a green screen or a related matting background. In this case, the lighting on the actor may often have to be chosen before the virtual backgrounds are finalized, posing difficulties for achieving consistent illumination between the actors and the background.